Draft-responsive controls for liquid fuel burners



Feb. 6, 1951 R. w. DE LANCEY 2,540,866-

DRAFT-RESPONSIVE CONTROL FOR LIQUID FUEL BURNERS Filed Aug. 31, 1948INVENTOR Pup m Dan/wear ZWM Patented Feb. 6, 1951 UNITED' PATENT OFFICEDRHFT RESPONSIVE CONTROLS FOR LIQUID FUEL BURNERS Ralph De; Lancey,Meriden, 001111., assignor to The Miller Company Meriden, Conn., acorporationof Connecticut Application August 31, 1948, Serial No. 46,971

The present invention; relates: toaburner: controls for'liquid fuel.burners; and.is.- more particularly directed toward controls for!intermittently operated gravity fed, liquid fuel burners under thecontrol of a remote switch, such. as a room thermostat or an immersionthermostat, with a fuel valve adapted: to beiopened and closed by suchthermostat; and employing forced draft produced by a motor drivenblowerwhi'ch operates continuously over long: periods where pilotignition is employed, or which operates ihtermittently where electricor: gas ignition is employed.

In such burners there is a. possibility that fuel supply may continue tothe burner eventhough the forced draft producing apparatus has not beenbrought into operation or for some reason has failed to function.

The present inventioncontemplates a system including a normally opensafety switch closeable by the moving stream of air employed for forceddraft, this switch being in series with the fuel valve controls.According" to the present invention; it is also-contemplated thatthesafety switch may be shunted bya normally closed switch under thecontrol of a time responsive element which opens the shunting switch atthe proper time.

The employ-merit of thepresent invention assures the presence of forceddraft whenever fuel is being fed to:the burner, except possibly duringthe starting period: when forced draftis not desired;

Otherand further objects will appear as the description proceeds;

The accompanying'drawingsshow, for purposes of illustrating the presentinvention; an embodiment in which the invention maytake' form; it beingunderstood" that the drawings are illustrative of the invention ratherthan limiting the same.

Inthe accompanying drawings:

Figure 1 is a side elevationa'l view illustrating an oilburner'installation with controls;

Figure 2'is an enlarged vertical sectional View through the safetyswitchshowing it -open;

Figure 3 is a still further enlarged sectional view showingtheswitchclosed; and

Figure 4 is an inverted plan view of the safety switch.

In the drawings, a pot type burneris illustrated generally at It], fuelsupply-pipeat H, and the forced draft duct at I2. Forceddraft is securedby blower'motor [3 operating a fan 14.

A combined constant level valve and metering valve of usualconstruction.isindicated at. l5. Through a pipe [6. and. fittings 11' it suppliesfuel to the supply. pipe U 'Ihevalvastructurel5 also includesa meteringvalve indicated at 8; Thisiis under the control of a bi-metal element ISwith electric heater 20.

Low voltage control current is obtained through a transformer Tconnected by a wire 2 l. The other side of the heater 2!) is connectedby a wire 22 with a fixed contact 23 of the safety switch S The otherside of the safety switch is connected by a wire 2 E. with the normallyopen contact 25 of the control thermostat 25. This thermostat isconnected with the transformer by wire 26'. A thermal heater 2'? isconnected between wire 2! and wire it. It is normally cold, but isheated whenever the thermostat 251 calls for burner operation. Thelei-metal element 28 is connected with wire 2-3 and through a switch 29and wire 3% with the wire 22, thereby provid ing circuit in shunt withthe safety switch S.

The safety switch S is a unitary structure having an insulating mountingplate so adapted to be placed over an opening 39' in the top wall of theduct I2 so that it is readily available for inspection and adjustment.-It carries a binding post 3| connected with wire 22, a binding post 32connected with wire 25, and an adjusting screw 33. The post 32 carries aconducting spring 34 which extends under the adjusting screw 33. Thisspring carries a U-shaped yoke to which is pivoted at at a rocker arm3'! carrying a vane 38. The other end of the arm 31 carries pins 39 inwhich is pivoted movable contact carrying arm 43. The movable contact isindicated at 4| in the form of a rounded button opposite the fixedcontact 23. The arm id is connected with pivot 36 by coiled spring if.The adjustment of the screw 33 determines the position of the vane atwhich the switch opens and closes.

The motor 13 operating the blower Id may be a continuously operatedmotor where pilot ignition is employed or may be an intermittentlyoperated motor where electric ignition is employed. When the motor i3isnot operating, the safety switch shifts to the open position, indicatedin Figure 2, on account of the weight of the vane, which biases thefever 3'! in a counterclockwise direction. This moves the pivot 39 highenough for the over-the'-center spring s2 to snap the movable contactarm down against a stop l3. The circuit of the safety switch is open inthe absence of forced draft.

Should the thermostat 25 call" for heat, a circuit will'beestablishedthrough the wire 21, heater 20', wire 3%, switch 29; bimetal" 28; to the thermostat 26 and wire 26. This will start heatingthebi-metal [9 which thereafter opens the metering valve l8. Currentwill also flow through the heater 21' andstart heating the bi-metal 28.The fan motor 13 is then started either manually orthrough suitabletiming controls set into operation by the thermostat ZS-so that ablastof air passes intotheburner. This blastof air reacts against the. vane38; lifts it. from the positionuof Figure 2 to the position of Figure 3.This car ries the pivot 39 below the spring 42 and causes the switch tosnap closed. 1 The closing of the safety switch S completes a secondcircuit for the heater 29 of the metering valve, so that the meteringvalve continues to be held open even though the bi-metal 29 has openedthe contact 29. Such opening takes place after a predetermined timewhich normally is sufficient for the blower to have been brought intooperation. If

for any reason the blower has not been brought into operation, the fuelvalve heater 29 will in due time have been disconnected by the switch 29and the flow of fuel stopped.

If for any reason the forced draft is not available because of powerfailure, motor failure or fan failure, the switchS will remain open sothat it is impossible to flood the burner or supply fuel when there isinadequate draft.

During the time that the blower is in operation, the vane 38 will moveback and forth slightly as indicated by the arrows at the left of Figure3, and this will cause a back and forth horizontal movement of thecontact 9! over the contact 23 as indicated by the short arrows nearthese elements. This serves to dislodge dirt particles which mightcollect and impair the low voltage circuit and to keep the contactsclean.

Since it is obvious that the invention may be embodied in other formsand constructions within the scope of the claims, I wish it to beunderstood that the particular form shown is but one of these forms, andvarious modifications and changes being possible, I do not otherwiselimit myself in any way with respect thereto.

What is claimed is:

i. In combination, a gravity fed, forced draft, liquid fuel burner, ametering valve for controlling flow of fuel to the burner and biasedtoward closed position, a fuel flow control circuit including a lowvoltage transformer, a condition responsive switch, an operator for themetering valve and a draft responsive switch all in series, a forceddraft blower, a duct connecting the blower to the burner, a leverextending lengthwise of the duct and pivotally mounted intermediate itsends, a vane carried by the end of the lever remote from the blower, thevane being biased by gravity toward a position to obstruct air flow andmovable upwardly by the air stream to a variable, less obstructingposition, a ductcarried, downwardly facing, fixed contact forming onepart of the draft responsive switch, a movable contact interconnectedwith the lever on the end opposite the vane and cooperable with thefixed contact to form the other part of the draft responsive switch, theinterconnections between the lever and movable contact including ahorizontal pivot which moves down and up as the vane moves up and downand an over-the center spring connecting the free end of the movablecontact and the pivot for the lever and acting, when above said pivot,to urge the movable contact upwardly, the movable contact moving acrossthe face of the fixed contact when the vane shifts position in its upperrange of movement so as to wipe dirt off the contacts and maintain thelow voltage circuit.

2.-'Ihe combination of claim 1, wherein the vane, the switch contactsand the snap spring are supported on an insulating member which coversan opening in the duct.

3. The combination of claim 1, having a normally closed switch in shuntwith the vane controlled switch, and a thermally responsive means foropening the. normally closed switch after a predetermined time wherebythe metering valve may be initially opened irrespective of bloweroperation.

4. The combination of claim 1, having means for vertically shifting thelever pivot to adjust the sensitivity of the switch.

5. In combination, a gravity fed liquid fuel burner, a fuel line leadingto the burner, an air duct for supplying air for combustion, a blowerconnected to the air duct to provide forced draft through the same tothe burner, a metering valve for supplying fuel to the fuel line, abimetallic operator for the metering valve, a heater for thebimetallicoperator, a low voltage source for the heater and two switchesin series with the heater, onebeing a condition responsive, thermallyoperated switch, the other a forced draft responsive switch mounted inthe air duct and including a lever pivoted on a horizontal axis in theduct and carrying at one end a vane which swings down under theinfluence of gravity and is lifted by the air stream from the blower,and at the other end a pivoted movable contact, an overthe-center springinterconnecting the lever and movable contact, and a ,fixed contactagainst which the spring holds the movable contact when the vane israised and over the surface of which it moves the movablecontact withmovement of the vane so long as it is high enough to keep the springaxis above the pivot of the movable contact, so that contact surfaces ofthe second switch are kept clean over long periods of blower operation.I

6. In combination, a gravity fed, forced draft, liquid fuel burnerhaving a forced draft blower and air duct which delivers a continuousblast of air characterized by small irregularities in velocity of theair' stream, a vane movably mounted in the duct, the vane being biasedin the absence of the air blast to a position to obstruct flow of air tothe burner and movable by the air stream to less obstructing positionswhich varywith the velocity of the air stream, a fixed contact in theduct, a movable, vane-operated contact in the duct, a snap spring whichsnaps the movable contact away from the fixed contact when the airstream is discontinued and holds the contacts in engagement when theblower is in operation, there being connections between the vane and themovable contact whereby the movement of the vane due to varying velocityof the air stream shifts the movable contact back and forth over thesurface of the fixed contact 'while the spring maintains the engagementof REFERENCES CITED The followingre'ferences are of record in the fileof this patent:

I UNITED STATES PATENTS Number Name Date Re. 21,950w Valiean Nov. 18,1941 2,197,746 irMatthes Apr. 6, 1940 2,237,041

Schreuder Apr..1, 1941 2,251,055 Howardet a1. July 29, 1941

